1. Field of the Invention
The present invention generally relates to fasteners, and more specifically, to mechanical fasteners suitable for permanently joining two or more panels together. The present invention also encompasses a method for permanently joining two or more panels using the fastener of the present invention in which an adhesive is used to permanently bond the fastener and panels together.
2. Description of the Prior Art
Numerous varieties of fasteners have been developed in response to the diversity of applications for which fasteners can be used. As manufacturing processes become more automated, there has been an increased emphasis on developing fasteners which simplify and facilitate assembly while simultaneously requiring that the fastener is capable of reliably securing the particular members being joined.
The particular type of fastener suitable for a given task is heavily dependent upon the characteristics of the structures being joined, such as their relative thicknesses and materials, and whether the joining is intended to be permanent or temporary. Conventionally, where a threaded fastener is used to join one member to another having a blind threaded hole, a self-locking fastener is often used. A self-locking fastener typically employs a plastic insert deposited in or on the threads of the fastener. The plastic insert increases the torque required to remove the fastener, yet provides a fastener that can be installed in a conventional manner. However, such self-locking fasteners are generally not suitable for joining thin members such as panels, nor are they considered a permanent fastener.
In contrast, rivets are a widely used type of permanent fastener for joining panels under conditions where disassembly is not anticipated, such as automotive door, body side, and undercarriage assemblies. Though suitable for many applications including joining either plastic or metal panels, rivets are not suitable for joining relatively thick members. Even when joining panels having a suitable thickness, the use of a standard (tubular) rivet is not generally feasible unless both sides of the joined panels are accessible so that a head, or clinch, can be formed on the rivet's shank opposite the rivet's preformed head.
With the development of modern adhesives such as epoxies and anaerobics, permanent retention of a threaded fastener in a bore can be achieved. An example of this approach is illustrated in U.S. Pat. No. 4,712,957 to Edwards et al. which teaches the use of a steel or aluminum fastener used to join a first member having a pre-drilled through hole with a second member having a pre-drilled blind hole. The shank of the fastener is shown to be either threaded or knurled with circumferential ridges. In addition, a number of longitudinal grooves are cut into the shank of the fastener. The grooves allow the forcible injection of a fluid adhesive into the blind hole while the fastener is partially inserted into the hole. As the fastener is further inserted into the hole, the adhesive fills the interstices between the fastener and the hole to achieve a secure bond. Consequently, the fastener is substantially more difficult to remove than it is to install. However, such a fastening system is unsuitable for joining panels where it is impracticable to provide a blind hole in the second member.
For joining thin members such as panels, both plastic and metal, various approaches have been suggested which often employ some form of barb. Barbs have long been used to prevent the removal of fasteners from the substrate in which they are embedded, as illustrated by the barbed nail taught by U.S. Pat. No. 1,918,936 to Shearman. However, the barb taught by Shearman is unsuitable for joining panels in that the barbs must become fully embedded in the members being joined to be functional. Similarly, U.S. Pat. No. 4,636,124 to Gugle et al. teaches a friction weld-type fastener having a pair of resilient wings which act to engage the interior surface of a bore into which the shank of the fastener is inserted. The frictional retention provided thereby offers a durable joining method in which it is possible to remove the fastener from the bore, though permanent damage to the resilient wings may result due to the fastener's plastic construction. The reliance on frictional retention also may result in loosening and/or rattles due to vibration. Again, the fastener taught by Gugle et al. is limited to use in a pre-drilled bore in thick members other than panels.
Variations on the resilient wings taught by Gugle et al. have found use in joining panels, such as the fasteners taught by U.S. Pat. No. 4,728,238 to Chisolm et al. and U.S. Pat. No. 4,551,189 to Peterson. Chisolm et al. teach a plastic fastener having numerous resilient wings extending obliquely from the fastener's shank. The wings allow the insertion of the fastener into a hole or bore with relative ease, while providing significantly greater resistance to the fastener's removal from the bore or hole. The fastener also overcomes one shortcoming of tubular rivets in that access to both sides of the joined panels is not required for assembly. However, the fastener is limited in its use in that it is formed from relatively weak plastic material and must be used with pre-drilled holes. Peterson illustrates a similar wing-type fastener of the type taught in U.S. Pat. No. 4,392,278 to Mugglestone.
From the above discussion, it can be readily appreciated that the prior art does not disclose a permanent fastener which is capable of joining two or more panels without access to both sides of the panels. Nor does the prior art teach or suggest a method which allows for the use of standard tooling to install such a fastener without the need for pre-drilled holes.
Accordingly, what is needed is a cost-efficient fastener for permanently joining two or more panels, such as automotive door, body side, and undercarriage assemblies, having as one feature the ability to form its own hole through the panels being joined, wherein access to the back side of the last panel is not required for the joining operation, and having the added benefit of providing a stable adhesive joint which will prevent rattles and squeaks between the panels.